The disclosure relates generally to rotary turbomachines, and more particularly, to a system and program product for controlling forces, pressures, and thrust against turbine rotors and their subcomponents.
Turbine systems can be used to generate mechanical or electrical power. Steam turbines, as one example, are highly efficient as the expansive force of steam is greater than many of the common gases used for powering turbines.
Greater operating efficiencies often require that high temperatures and high pressures be used. In turn, robust operation of turbines under these conditions can be problematic. For example, previous steam turbine solutions have used inlet temperatures and pressures of 760° C. (1400° F.) and 38.6 MPa (5600 psi). Other common conditions for a modern boiler and steam turbine system can be approximately 565° C. (1050° F.) and 16.5 MPa (2400 psi). These turbine systems sometimes incorporate “reheat,” referring to one or more process steps where steam reenters a boiler for one or more stages of heat addition.
Typically, the first turbine section downstream of the boiler and upstream of the reheat is referred to as the high pressure (HP) turbine section. Exhaust steam from the high pressure (HP) turbine section is sent to the boiler for reheating along a cold reheat line. The reheated steam can be heated to the initial inlet temperature before flowing into an intermediate pressure (IP) turbine section. Exhaust from the IP turbine enters and flows through the low pressure (LP) turbine before exiting as exhaust to the condenser. Some systems may not incorporate the IP section, and more complex systems may have multiple reheat stages. Physical design of the system can vary, depending on the application. Several turbine sections can reside within the same casing, or multiple casings may exist.
A main output shaft and an area proximate to the spinning steam turbine rotor can each include bearings designed to handle high temperatures and high pressures. These bearings can include internal oil seals located between the bearing and the output shaft. In addition, a “thrust fitting” can absorb the axial load developed by the power train. Bearings and thrust fittings can be held in place, or held in a limited range of movement, by axial thrust forces and/or hydraulic forces of oil in the bearing. This thrust force can be created through a combination of the fluid inertia acting on the turbine buckets, and the pressure developed by variation in cross-sectional area acting against portions of the system. As the respective bearings or thrust fittings may only withstand certain temperatures and pressures of a corresponding gas (e.g., steam) or operating fluid, the thrust pressure applied and resultant from the steam should be within permissible temperature and pressure levels.
Additional considerations associated with thrust fittings are that thrust fittings do not readily accept multiple and repeated directional changes in thrust, and that a turbine can become unstable when the amount of resultant thrust acting on a rotor or its subcomponents approaches zero. As a result, thrust fittings are designed to be pressurized in a stable manner from one direction or the other; their ability to rapidly absorb directional reversals in thrust is limited.